It was reasonable for the small Sea Cap XII to follow the inner route. Although spanned by several bridges, the inner route would not require the tug and tow to leave the river, navigate the open waters of the Strait of Georgia, and re-enter the river at Point Grey. As the size and nature of the tow did not seem to present any restrictions, and the tug was handled by an experienced skipper who had transited the river with this and other tows on many occasions, the manager of the towing company did not hesitate to assign the Sea Cap XII to complete this short towing job. Notwithstanding that the owners believed that the tow would be conducted down the south arm of the river, it could not be determined whether there was a clear agreement between the owners and the towing company over the route to be followed. A clear understanding by the owners and the towing company might have prompted them to more carefully examine all aspects of the transit plan. The final decision as to the readiness of the tow was left in the hands of the skipper of the Sea Cap XII. He was aware of his responsibility, and that he could refuse to start the tow. However, a lack of written procedures and the absence of a clear understanding between the companies stipulating the essential components of the job, including the route to follow, reduced the overall safety of the operation. Using the calculated height of tide at Sand Heads (12.2feet), the clearance under the Knight Street Bridge at the time of striking is calculated to have been 20.84m, approximately 6cm (0.2feet) lower than that given in the North Fraser Harbour Commission sheet. Whatever the exact clearance may have been, it was not noted by any of those involved in the operation; the boom was not positioned with regard to the bridge's clearance, nor was its height checked against the data. As the tow moved down the North Arm of the Fraser River, there was one final opportunity to note the impending lack of clearance under the Knight Street Bridge. This was the difference in clearances between the Queensborough and Knight Street bridges. The tug and tow passed under the Queensborough Bridge less than one hour before hitting the Knight Street Bridge. The clearance under the Queensborough Bridge is approximately three metres greater than the clearance under the Knight Street Bridge. The boom first contacted the side of the Knight Street Bridge; from this it can be deduced that the top of the boom must have passed within three metres of the underside of the Queensborough Bridge. Such a close pass, if observed from the tug below, would almost certainly have led the crew to reassess the situation. However, neither the skipper nor the deck-hand attended to this aspect of the operation, and so this available clue was lost. The skipper was concentrating on conning the tug, and the deck-hand did not assume that he had a responsibility to observe the boom end and, if necessary, warn the skipper. The towing company policy and, specifically, the lack of clear rules and job descriptions, allowed the tug crew to apply their own, custom-formed measures when performing their tasks. In most cases their experience and on-the-job training were satisfactory. However, such a system can fail - and lead to an accident - when a not-so-typical task comes along, or when one of those involved fails to examine all aspects of the task. In this instance, the owners of the barge, and the towing company, and the crew of the tug all relied on the others to verify that the barge had sufficient air draft to safely complete the voyage.Analysis It was reasonable for the small Sea Cap XII to follow the inner route. Although spanned by several bridges, the inner route would not require the tug and tow to leave the river, navigate the open waters of the Strait of Georgia, and re-enter the river at Point Grey. As the size and nature of the tow did not seem to present any restrictions, and the tug was handled by an experienced skipper who had transited the river with this and other tows on many occasions, the manager of the towing company did not hesitate to assign the Sea Cap XII to complete this short towing job. Notwithstanding that the owners believed that the tow would be conducted down the south arm of the river, it could not be determined whether there was a clear agreement between the owners and the towing company over the route to be followed. A clear understanding by the owners and the towing company might have prompted them to more carefully examine all aspects of the transit plan. The final decision as to the readiness of the tow was left in the hands of the skipper of the Sea Cap XII. He was aware of his responsibility, and that he could refuse to start the tow. However, a lack of written procedures and the absence of a clear understanding between the companies stipulating the essential components of the job, including the route to follow, reduced the overall safety of the operation. Using the calculated height of tide at Sand Heads (12.2feet), the clearance under the Knight Street Bridge at the time of striking is calculated to have been 20.84m, approximately 6cm (0.2feet) lower than that given in the North Fraser Harbour Commission sheet. Whatever the exact clearance may have been, it was not noted by any of those involved in the operation; the boom was not positioned with regard to the bridge's clearance, nor was its height checked against the data. As the tow moved down the North Arm of the Fraser River, there was one final opportunity to note the impending lack of clearance under the Knight Street Bridge. This was the difference in clearances between the Queensborough and Knight Street bridges. The tug and tow passed under the Queensborough Bridge less than one hour before hitting the Knight Street Bridge. The clearance under the Queensborough Bridge is approximately three metres greater than the clearance under the Knight Street Bridge. The boom first contacted the side of the Knight Street Bridge; from this it can be deduced that the top of the boom must have passed within three metres of the underside of the Queensborough Bridge. Such a close pass, if observed from the tug below, would almost certainly have led the crew to reassess the situation. However, neither the skipper nor the deck-hand attended to this aspect of the operation, and so this available clue was lost. The skipper was concentrating on conning the tug, and the deck-hand did not assume that he had a responsibility to observe the boom end and, if necessary, warn the skipper. The towing company policy and, specifically, the lack of clear rules and job descriptions, allowed the tug crew to apply their own, custom-formed measures when performing their tasks. In most cases their experience and on-the-job training were satisfactory. However, such a system can fail - and lead to an accident - when a not-so-typical task comes along, or when one of those involved fails to examine all aspects of the task. In this instance, the owners of the barge, and the towing company, and the crew of the tug all relied on the others to verify that the barge had sufficient air draft to safely complete the voyage. The end of a crane boom on the barge T.L. Sharpe hit the span of the Knight Street Bridge. The crane shifted off the barge's deck and sank under the bridge. The impact of the crane damaged the bridge, which was subsequently closed to traffic for two days. No one involved in transportation of the crane assessed the height of the boom prior to the towing operation. The crew of the tug did not observe the height of the tow while passing under the Queensborough bridge. The towing company had not established any written operational procedures to be observed by the tug crews. There was no clear understanding among the tug owner, tug operator, and barge owner over which route the tow would take.Findings The end of a crane boom on the barge T.L. Sharpe hit the span of the Knight Street Bridge. The crane shifted off the barge's deck and sank under the bridge. The impact of the crane damaged the bridge, which was subsequently closed to traffic for two days. No one involved in transportation of the crane assessed the height of the boom prior to the towing operation. The crew of the tug did not observe the height of the tow while passing under the Queensborough bridge. The towing company had not established any written operational procedures to be observed by the tug crews. There was no clear understanding among the tug owner, tug operator, and barge owner over which route the tow would take. The boom of the crane struck the span of the Knight Street Bridge because the air draft of the tow was not ascertained prior to commencing the tow. Contributing to the occurrence was the lack of a clear understanding of the tug owner, tug operator and barge owner of the route the barge was expected to take.Causes and Contributing Factors The boom of the crane struck the span of the Knight Street Bridge because the air draft of the tow was not ascertained prior to commencing the tow. Contributing to the occurrence was the lack of a clear understanding of the tug owner, tug operator and barge owner of the route the barge was expected to take. As a result of the accident in March 1993, the barge owners initiated standard verbal communication procedures with contracted towing companies. Following this second occurrence, the owners of the barge and crane have initiated steps to develop more-formal written procedures for communicating with towing companies. When a towing order is placed, the dimensions of the tow, including its height, will be explicitly communicated to the towing party.Safety Action As a result of the accident in March 1993, the barge owners initiated standard verbal communication procedures with contracted towing companies. Following this second occurrence, the owners of the barge and crane have initiated steps to develop more-formal written procedures for communicating with towing companies. When a towing order is placed, the dimensions of the tow, including its height, will be explicitly communicated to the towing party.